Vestibular testing apparatus

ABSTRACT

A system for detecting and recording head orientations of a person includes: a first sensor device capable of providing sensor data regarding a head orientation of a person in a three-dimensional space; a medical data acquisition system configured for storing and outputting the sensor data from the first sensor device; and a processor configured for processing the sensor data from the medical data acquisition system, outputting a first signal representing the head orientation, and generating an image for presentation by a graphical display; wherein the image comprises: a first reference indicator; an orientation indicator, wherein a position of the orientation indicator in the image is determined based on the first signal from the processor, and a feedback indicator when a first condition is met.

RELATED APPLICATION DATA

This application claims priority to and the benefit of Danish patentapplication No. PA 2015 70187, filed Mar. 30, 2015, pending, andEuropean patent application No. 15161784.2, filed Mar. 30, 2015,pending. The entire disclosures of both of the above applications areexpressly incorporated by reference herein.

FIELD

This disclosure relates to an apparatus for diagnosing and treatingvertigo, dizziness and similar balance-related disorders in a humanbeing.

BACKGROUND

Dizziness is a common condition affecting a large part of thepopulation. The diagnostic and treatment for vestibular disordersrequires that a patient be placed with their head in particularpositions, e.g. the patient is sitting upright with the head straightand not moving. In order to perform diagnosis or treatment the patientmay need to be moved to a particular position or to a predetermined setof positions in a specific order. The proper positioning of thepatient's head is essential for proper diagnosis and treatment.

Since vestibular activity (i.e. a person's reaction to changes inorientation, “sense of balance”) cannot be monitored directly in apatient, a physician has to rely on secondary indications, such as theeye movement reflex, for objectively detecting activity in a person'svestibular system. When the head rotates about any axis, a person willinherently and involuntarily try to sustain distant visual images byrotating his or her eyes in the opposite direction on the respectiveaxis. The semi-circular canals in the inner ear sense angular momentumand send signals to the nuclei for eye movement in the brain. From here,a signal is relayed to the extraocular muscles to allow his or her gazeto fixate on one object as the head moves. A particular reaction denotednystagmus occurs when the semi-circular canals are being stimulatedwhile the head is not in motion. The direction of eye movement isdirectly related to the particular semi-circular canal being stimulated.

One example of a condition which may be diagnosed and treated is BenignParoxysmal Positional Vertigo (BPPV). BPPV is the most common cause ofvertigo, accounting for nearly 40% of all vertiginous patients. The mostcommon cause for BPPV is a displacement of the calcium-carbonatedcrystals (otolithic stones) present in the utricle into thesemi-circular canal (canalithiasis) or onto the cupula (cupulathiasis)of the patient. Today, posterior canal BPPV (the most common) isdiagnosed by performing a special sequence of particular positionings ofthe patient denoted a Dix-Hallpike maneuver, while the examinersimultaneously looks for nystagmus by observing the eyes when thepatient is in a supine position with his or her head turned towards theaffected ear. The Dix-Hallpike maneuver is the most common positioningsequence in use for diagnosing BPPV but other maneuvers such asHallpike-Stenger, side-lying and roll are also used. The maneuver chosenis determined by physician preference, patient's neck mobility and asuspicion of whether the BPPV is present in the posterior, anterior orlateral semi-circular canal, respectively. The treatment for BPPV isthrough a repositioning maneuver. There are several repositioningmaneuvers available to the physician for this purpose, e.g. CanalithRepositioning Treatment (denoted the Epley maneuver), Liberatory(denoted the Semant maneuver) and the so-called BBQ roll maneuver.

The maneuvers are successful in 90% of all patients treated in thismanner. However, nearly 40% of the treated patients do experiencereoccurrences and may need to return to the physician for additionalrepositioning. Why almost 40% of the treated patients do not experienceimmediate or lasting success from the treatment is not known. One reasoncould be that the repositioning maneuver may not have been properlyperformed by the physician. If the physician had the means to performthe repositioning maneuver at his disposal while at the same timekeeping track of the patient's position and response, then therepositioning maneuver could be performed with a higher degree ofconfidence by the physician and a lot more patients would thusexperience success from the treatment.

SUMMARY

A method may be performed for observing and identifying abnormal humanvestibular activity. The method may involve invoking a selected spatialorientation in a person and providing a visual representation of thespatial orientation of the person and one or more motion components ofthe vestibular activity of the person. The method may permit theautomatic performance of e.g. the Dix-Hallpike maneuver while monitoringthe vestibulo-spinal reflex as an indication of the change in spatialorientation together with monitoring the spatial orientation. Anapparatus may be configured to perform the above method, and may includepositioning or orientation measurement for determining the position of apatient's head, e.g. accelerometers or similar devices, and eye movementmonitoring equipment, e.g. goggles or glasses mounted on the head of thepatient and provided with cameras or similar equipment in order toregister eye movements of the patient. In some cases, the apparatus mayfurther comprise a mechanism for suspending the patient in a freelyrotatable, arbitrary 360° spatial orientation during the performance ofthe test, the mechanism being capable of altering the spatialorientation of the patient automatically according to the requirementsfor triggering the desired response during the test.

The apparatus described above may demand a fair degree of training andexperience by the physician or assistant performing the test insituations where there is no mechanism for automatically altering thespatial orientation of the patient. Even if such mechanism is available,it may be bulky and expensive, and may thus only be accessible tophysicians having the necessary space and funding to obtain and use sucha mechanism.

Thus, it may be desirable to have a cost-effective method and a systemfor observing and identifying abnormal human vestibular activity duringtesting or treatment which is easy to use by a physician with a minimumof additional training without taking up a lot of space.

According to some embodiments, a system for detecting and recording headorientations of a person is devised, said system comprising a firstsensor device capable of acquiring at least sensor data regarding aperson's head orientation in three-dimensional space, a computing systemcomprising, a medical data acquisition system, a processor, and agraphical display, wherein the medical data acquisition system isconfigured for storing and outputting sensor data from the first sensordevice, the graphical display is configured for displaying imagesgenerated by the processor, and the processor is configured forprocessing the sensor data from the medical data acquisition system,outputting a first signal representing head orientation and generatingimages suitable for being shown by the graphical display, said imagescomprising at least; a first reference indicator, an orientationindicator, wherein the position of said orientation indicator, e.g. withrelation to the first reference indicator, in the graphical display isdetermined based on the first signal from the processor, and a feedbacksignal whenever a first specific condition is met. This allows aphysician to follow manipulations of the orientation of the person in aprecise and secure way without involving the use of bulky equipment orelaborate training.

In one embodiment, the first specific condition is that the first signalrepresenting a head orientation deviates more than a predeterminedamount from a head orientation according to a particular manoeuvringscheme. In another embodiment, the first specific condition is that theorientation indicator deviates more than a predetermined amount from adesired position with relation to the first reference indicatoraccording to a particular manoeuvring scheme. This allows the display ofthe system to provide fast and effective feedback to the physicianduring the performance of head movements of the person being examined ortreated.

In an embodiment, the processor generates the feedback signal bychanging the color, the shape or the size of the orientation indicatorin the graphical display. In an embodiment, the system comprises amemory configured for holding at least a stored, three-dimensional modelof a human head. In a further embodiment, the images generated by theprocessor comprises a two-dimensional projection of the stored,three-dimensional model of a human head, wherein the viewing angle ofthe two-dimensional projection is determined based on the first signalrepresenting head orientation. In another embodiment, the firstreference indicator is configured for providing feedback regardingrotations about a first local axis, and a second reference indicator isconfigured for providing feedback regarding rotations about a secondlocal axis perpendicular to the first local axis. The feedback signaltogether with the changes in the viewing angle of the two-dimensionalprojection of the three-dimensional model of a human head makes it easyfor the physician to follow the orientation of the person's headcontinuously during examination and immediately correct any deviationsfrom the predetermined head rotation.

In an embodiment, the system comprises a second sensor device capable ofacquiring sensor data regarding a person's eye movements, and theprocessor is configured for deriving vestibular activity from the sensordata regarding a person's eye movements provided by the second sensordevice. In further embodiments, the stored, three-dimensional model of ahuman head of the memory comprises stored, three-dimensional models of aleft set of semi-circular canals and a right set of semi-circularcanals, respectively. The processor, in an embodiment, is configured toprovide a two-dimensional projection of the stored, three-dimensionalmodels of the sets of semi-circular canals and to change the color ofthe individual semi-circular canals of the left set of semi-circularcanals and the right set of semi-circular canals, respectively, inresponse to the derived vestibular activity. The two-dimensionalprojections of the models of the semi-circular canals of the left set ofsemi-circular canals and the right set of semi-circular canals,respectively, changes their viewing angle with the viewing angle of thetwo-dimensional projection of the three-dimensional model of a humanhead and, in addition, changes their appearance individually whenevervestibular activity is detected by the acquired data regarding theperson's eye movements, e.g. by changing color. This feature allows thephysician to follow vestibular activity of the person being examined ortreated during head manipulations, thus making it easier for thephysician to determine abnormal vestibular responses from the personduring examination or treatment.

In some embodiments, the particular manoeuvring scheme is selected fromthe group consisting of a Dix-Hallpike maneuver, an Epley maneuver or aSemant maneuver. An embodiment provides the particular manoeuvringscheme is selected prior to detecting vestibular activity in a person.This feature allows the physician to select, e.g. a Dix-Hallpikemaneuver prior to performing it on the person being examined and to havethe system aid the individual movements of the maneuver precisely and inthe correct sequence, since the system is capable of ‘knowing’ inadvance that a Dix-Hallpike maneuver is to be performed, provide asequence of expected head-turning angles for guidance and thus possessesthe capability to guide the physician during performance of themaneuver.

A system for detecting and recording head orientations of a personincludes: a first sensor device capable of providing sensor dataregarding a head orientation of a person in a three-dimensional space; amedical data acquisition system configured for storing and outputtingthe sensor data from the first sensor device; and a processor configuredfor processing the sensor data from the medical data acquisition system,outputting a first signal representing the head orientation, andgenerating an image for presentation by a graphical display; wherein theimage comprises: a first reference indicator; an orientation indicator,wherein a position of the orientation indicator in the image isdetermined based on the first signal from the processor, and a feedbackindicator when a first condition is met.

Optionally, the first condition is met when the head orientationrepresented by the first signal deviates more than a predeterminedamount from a desired orientation according to a manoeuvring scheme.

Optionally, the manoeuvring scheme comprises a Dix-Hallpike maneuver, anEpley maneuver, or a Semant maneuver.

Optionally, the manoeuvring scheme is pre-determined prior to detectingvestibular activity in the person.

Optionally, the first condition is that the position in the image of theorientation indicator deviates more than a predetermined amount from adesired position in the image with relation to the first referenceindicator according to a manoeuvring scheme.

The first reference indicator may be formed like a ruler or a numberline with numbers along the ruler or number line showing a signeddistance from the number in question to a reference point marked withthe number zero on the ruler or number line. The number may show indegrees, the angular rotation of the head around a first axis, forexample a horizontal axis in which case the first reference indicator ispreferably shown as a horizontal ruler or number line in the image. Theorientation indicator may be positioned with relation to the firstreference indicator at a position that corresponds to the currentangular rotation of the head around the first, e.g. horizontal, axis.The first condition may be met, when the orientation indicator isoutside a desired range of angular rotation around the first axis.

Optionally, the image comprises a second reference indicator.

The second reference indicator may be formed like a ruler or a numberline with numbers along the ruler or number line showing a signeddistance from the number in question to a reference point marked withthe number zero on the ruler or number line. The number may show indegrees, the angular rotation of the head around a second axis. Thesecond axis may be perpendicular to the first axis. The second axis maybe a vertical axis in which case the second reference indicator ispreferably shown as a vertical ruler or number line in the image. Theorientation indicator may be positioned with relation to the secondreference indicator at a position that corresponds to the currentangular rotation of the head around the second, e.g. vertical axis. Thefirst condition may be met, when the orientation indicator is outside adesired range of angular rotation around the second axis, or the firstcondition may be met, when the orientation indicator is outside adesired range of angular rotation around the first axis and/or isoutside a desired range of angular rotation around the second axis.

Optionally, the orientation indicator may have the form of an image of aCartesian coordinate system, e.g., with the x-axis, y-axis, and z-axisdefined below with relation to a person's head, and the orientation ofwhich may be shown in the image with relation to another Cartesiancoordinate system forming the first reference indication and, e.g.,having a horizontal x-axis and a horizontal y-axis and a verticalz-axis, e.g. corresponding to a desired starting position of theperson's head of a selected manoeuvring scheme. Thus, optionally, at thedesired starting position of the person's head, the orientationindicator and the first reference indicator coincide, and the as theperson's head is rotated desirably in accordance with the selectedmanoeuvring scheme, the orientation indictor is shown in the image inpositions corresponding to the current rotation of the person's head,and the first condition may be met when the orientation indicator isoutside a desired range of angular rotation, e.g., around the x-axis,y-axis and z-axis.

Optionally, the feedback indicator comprises a change in a color, ashape, or a size of the orientation indicator.

Optionally, the system further includes a memory configured for storinga three-dimensional model of a human head.

Optionally, the feedback indicator comprises a change in a color, ashape, or a size of (1) a two-dimensional projection of thethree-dimensional model of the human head, (2) the first referenceindicator or (3) a second reference indicator.

Optionally, the three-dimensional model of the human head comprises afirst three-dimensional model of a left set of semi-circular canals anda second three-dimensional model of a right set of semi-circular canals.

Optionally, the image generated by the processor comprises atwo-dimensional projection of the three-dimensional model of the humanhead, wherein a viewing angle of the two-dimensional projection isdetermined based on the first signal representing the head orientation.

Optionally, the image generated by the processor comprises a secondreference indicator.

Optionally, the first reference indicator is configured for providing afirst feedback regarding a first rotation about a first local axis, andthe second reference indicator is configured for providing a secondfeedback regarding a second rotation about a second local axisperpendicular to the first local axis.

Optionally, the system further includes a second sensor device capableof providing an additional sensor data regarding an eye movement of theperson, wherein the processor is configured for deriving vestibularactivity from the additional sensor data regarding the eye movementprovided by the second sensor device.

Optionally, the system further includes a memory configured for storinga three-dimensional model of a human head; wherein the three-dimensionalmodel of the human head comprises a first three-dimensional model of aleft set of semi-circular canals, and a second three-dimensional modelof a right set of semi-circular canals; and wherein the processor isconfigured to (1) provide a two-dimensional projection of the firstthree-dimensional model, the second three-dimensional mode, or both, and(2) to change a color of at least a part of the two-dimensionalprojection in response to the derived vestibular activity.

Optionally, the system further includes the graphical display.

One or more embodiments described herein provide a cost-effective methodand a system for observing and identifying abnormal human vestibularactivity during testing or treatment, which is easy to use by aphysician with a minimum of additional training without taking up a lotof space. Accordingly, one or more embodiments described herein areadvantageous over known apparatus and method, like those described inU.S. Pat. No. 6,800,062.

Other features and embodiments will be described below in the detaileddescription.

DESCRIPTION OF THE FIGURES

The embodiments are described in greater detail in the following, where

FIG. 1 is a block schematic illustrating a vestibular testing apparatus,

FIG. 2 illustrates an exemplary display showing a vestibular responseand head direction,

FIG. 3a illustrates a direction target in a correct position during ahead movement, and

FIG. 3b illustrates a direction target in an incorrect position during ahead movement.

DETAILED DESCRIPTION

Various embodiments are described hereinafter with reference to thefigures. Like reference numerals refer to like elements throughout. Likeelements will, thus, not be described in detail with respect to thedescription of each figure. It should also be noted that the figures areonly intended to facilitate the description of the embodiments. They arenot intended as an exhaustive description of the claimed invention or asa limitation on the scope of the claimed invention. In addition, anillustrated embodiment needs not have all the aspects or advantagesshown. An aspect or an advantage described in conjunction with aparticular embodiment is not necessarily limited to that embodiment andcan be practiced in any other embodiments even if not so illustrated, orif not so explicitly described.

The block schematic in FIG. 1 illustrates a clinical setup 1 for testingand examining vestibular activity in a person. The clinical setup 1comprises a computerized system 2, an eye movement detector 6 fordetecting movements of an eye 5 of the person being examined, anorientation sensor 4 for detecting the orientation of the person, and adisplay 3 for displaying orientation and vestibular activity in realtime during an examination. The computerized system 2 comprises a dataacquisition module 7, a calculation module 8, a memory 9 holding athree-dimensional model of a head and semi-circular canals of a person,and a graphic processor 10 for providing an output signal for thedisplay 3. The computerized system 2 may be embodied as a dedicatedcomputing device or it may be embodied as an application designed forexecution on a standard off-the-shelf personal computer.

The eye movement detector 6 and the orientation sensor 4 may be builtinto a self-contained, head-mountable unit (not shown in FIG. 1), e.g.of the kind described in European patent application EP 14169653.4. Thehead-mountable unit is a relatively small and lightweight piece ofhardware allowing a person to move his or her head freely while wearingthe unit. The head-mountable unit may preferably be embodied as a pairof goggles fixable to a person's head by e.g. an adjustable headband.The eye movement detector 6 may be embodied as a small video cameraconstantly monitoring the eye of the person, e.g. via a semi-transparentmirror. The eye movement detector 6 may be doubled for the purpose ofmonitoring movement of both the left eye and the right eye of a personsimultaneously. The orientation sensor 4 may be embodied as anaccelerometer unit mounted on the head-mountable unit. Duringexamination, the head-mountable unit is fixed to the head of the personbeing examined, and data regarding eye movements and spatial orientationare fed to the data acquisition module 7 of the computerized system 2.Prior to performing a proper examination of the person, an orientationcalibration procedure is performed in order to be able to coordinate thedata collected from the head-mountable unit correctly with a referenceequilibrium position of the person.

During an examination of the person wearing the calibrated,head-mountable unit, the person's head is placed in a series ofdifferent positions or orientations by the physician performing theexamination while the physician watches the display 3 of the clinicalsetup 1. By looking at the display 3 during the examination thephysician may monitor the actual orientation and the vestibularreactions of the person being examined. The vestibular reactions arereflected in involuntary movements of the eyeballs of the person and thedata from the eye movement detector 6 are thus used by the calculatingmodule 8 for calculating the corresponding vestibular reactions. Theresults of the calculations are provided to the graphic processor 10 andcombined with a stored, three-dimensional model of a human head and apair of associated semi-circular canals provided by the dedicated memory9 for the purpose of generating a real time, two-dimensional perspectiveprojection of a human head and semi-circular canals in a viewport of thedisplay 3 for viewing by the physician performing the examination.

An exemplary picture, as it may be provided by the display 3 of FIG. 1,is illustrated in FIG. 2. FIG. 2 shows a main window 20 comprising aperspective projection of a human head 21, a data window 28, a set ofoperating controls 29, 30, 31, 32 and a set of tabbed windows 33, 34, 35and 36. The perspective projection of the human head 21 furthercomprises a set of left semi-circular canals 22L, a set of rightsemi-circular canals 22R, a horizontal reference indicator 25, e.g.constituting an example of the first reference indicator, a verticalreference indicator 26, e.g. constituting an example of the secondreference indicator, and an orientation indicator 27. The orientationindicator 27 represents a two-dimensional projection of the headorientation of the person as determined by the orientation sensor 4. Inthe perspective projection 21, the left set of semi-circular canals 22Lhas a posterior semi-circular canal 23 and an anterior semi-circularcanal 24 emphasized by a dark color indicating vestibular activity inthose canals. For clarity, the left and right sets of semi-circularcanals 22L and 22R, respectively, are shown as floating in space somedistance from the human head 21 in the main window 20.

During use of the system 1, the physician initiates a data collectionsession by calibrating the head-mountable unit by activating the“Center” button 29 in the main window 20. This calibration is done withthe person's head carrying the head-mountable unit and facing straightforward. Any subsequent movements the person's head makes aftercalibration is then recorded and shown relative to the calibrationpoint. When the person moves his or her head in space, the perspectiveprojection angle of the human head 21 moves correspondingly in the mainwindow 20, the perspective projection angle of the set of leftsemi-circular canals 22L and the set of right semi-circular canals 22Rmoving along with the human head 21 while keeping their relativepositions with respect to the human head 21. When the calibrationprocedure has finished, the physician may start the acquisition ofmovement and vestibular response data by activating the “Start” button30 in the main window 20.

Moving together with the perspective projection of the human head 21 isthe orientation indicator 27. When the person's head moves, theorientation indicator 27 will move correspondingly with respect to thevertical reference indicator 26 and the horizontal reference indicator25, respectively. The positioning of the vertical reference indicator 26and the horizontal reference indicator 25 is determined by the type ofexamination to be performed. In the case of e.g. the physician wishingto perform a Dix-Hallpike maneuver with the aid of the system 1, thephysician has to move the person's head about an axis going verticallythrough the head of the person in a first move and about an axis goingfrom ear to ear of the person in a second move. The orientationindicator 27 aids the physician in performing the Dix-Hallpike maneuverby making the physician move the person's head in such a way that theorientation indicator 27 stays on the vertical reference indicator 26during the first movement and the orientation indicator 27 stays on thehorizontal reference indicator 25 during the second movement.Preferably, orientation indicator 27 may light up or change color if theorientation indicator 27 is veering off track during the first or thesecond movement. An angle tolerance may be built into the system.

In this way, the display 3 of the system 1 may provide positive feedbackto the physician in real time during performance of e.g. theDix-Hallpike maneuver, guiding the movements the physician has toperform on the patient's head and/or torso in order to retrieve thedesired examination or treatment results. The combination of thetwo-dimensional projection of the head 21, the two sets of semi-circularcanals 22L and 22R and the orientation indicator 27 with respect to thevertical reference indicator 26 and the horizontal reference indicator25 provides for a high degree of precision in the movements of theperson's head. Due to the fact that the eye movement detector 6 ismonitoring the eyes of the person, the system may indicate e.g. thepresence of nystagmus by making individual semi-circular canals of thetwo-dimensional projection of the semi-circular canals 22L and 22R lightup or change color in the window 20, thus indicating vestibular activityin those semi-circular canals. This is indicated in FIG. 2 as the leftposterior semi-circular canal 23 and the left anterior semi-circularcanal 24 being dark in color indicating activity in the left posteriorsemi-circular canal and the left anterior semi-circular canal of theperson being examined.

Some types of examination may require the person being tested to bevision denied, i.e. blindfolded. This is due to the fact that it isnatural to most people to use their eyesight in order to determine theirorientation in space. In order to exclude this sensory modality from theexamination, the person being examined may wear dark or opaque eyecoverings on one or both eyes during examination or treatment. The eyecoverings are preferably placed beneath the goggles when worn by theperson and are manufactured from a material blocking all light but theinfrared range of the electromagnetic spectrum, thus rendering theperson without any visual cues for the duration of the examination. Theeye movement detector 6 of the system 1 is configured to be sensitive inthe infrared range of the spectrum, thereby permitting detection of eyemovements even though the person being examined cannot see anything.Since the balance reflex of the eyes is present even if the person doesnot see anything, this strategy of examination effectively excludesvisual cues from the examination, thus effectively isolating the signalsfrom the balance organs for detailed analysis during or after theexamination.

During an examination, the data acquisition module 7 of the computerizedsystem 2 in FIG. 1 provides the calculation module 8 with streams ofreal time data representing gaze direction and spatial orientation ofthe head of the person being examined. These data are sorted, filteredand recorded by the calculation module 8 and converted into a vectorrepresenting spatial orientation and vestibular activity in both sets ofsemi-circular canals 22L and 22R, respectively. This vector is providedto a first input of the graphic processor 10 for the generation of thereal time two-dimensional projection of a human head 21 shown in FIG. 2.Simultaneously, the stored three-dimensional model of a human head andassociated semi-circular canals provided by the dedicated memory 9 isapplied to a second input of the graphic processor 10 for calculatingthe projection of a proper two-dimensional representation of a humanhead 21 and corresponding left and right sets of semi-circular canals22L and 22R, respectively, suitable for being shown on the display 3.

A three-dimensional coordinate system is defined as a standardright-hand coordinate system, where the x-axis goes from ear to ear in aperson's head, the y-axis goes from the top of the person's parietalbone through the neck, and the z-axis goes from the back of the person'shead to the tip of the nose. This coordinate system will be referred toin the following. Orientation angles of a human head about the threeaxes x, y and z may be expressed as Tait-Bryan chained rotations usingthree rotational matrices, where

${{{\overset{\rightarrow}{M}}_{x}(\alpha)} = \begin{bmatrix}1 & 0 & 0 \\0 & {\cos \; \alpha} & {{- \sin}\; \alpha} \\0 & {\sin \; \alpha} & {\cos \; \alpha}\end{bmatrix}},{{{\overset{\rightarrow}{M}}_{y}(\beta)} = \begin{bmatrix}{\cos \; \beta} & 0 & {{- \sin}\; \beta} \\0 & 1 & 0 \\{\sin \; \beta} & 0 & {\cos \; \beta}\end{bmatrix}}$ and${{\overset{\rightarrow}{M}}_{z}(\gamma)} = {\begin{bmatrix}{\cos \; \gamma} & {{- \sin}\; \gamma} & 0 \\{\sin \; \gamma} & {\cos \; \gamma} & 0 \\0 & 0 & 1\end{bmatrix}.}$

The three rotational angles α, β, and γ expressed in radians, describethe rotation of a human head about the three axes with respect to theorigin (set at calibration time). Data provided by the rotation sensor 4in FIG. 1 is used to calculate the rotation angles of the head of theperson being examined. At calibration time, the rotational angles α, β,and γ are zero, and the data from the rotation sensor 4 is expressed asa vector, thus:

${\overset{\rightarrow}{M}}_{cal} = {\begin{bmatrix}\alpha \\\beta \\\gamma\end{bmatrix} = \begin{bmatrix}0 \\0 \\0\end{bmatrix}}$

at calibration time, and

${\overset{\rightarrow}{M}}_{x,y,z} = \begin{bmatrix}\alpha \\\beta \\\gamma\end{bmatrix}$

during examination. The vector {right arrow over (M)}_(x,y,z) isgenerated from data from the rotation sensor 4 by the data acquisitionmodule 7, and is used as input for the calculation module 8.

Anatomically, the three semi-circular canals of a human being aredenoted the lateral semi-circular canal (operating around a verticalaxis in the transversal plane), the anterior semi-circular canal(operating around an anterial-posterial axis in the coronal plane) andthe posterior semi-circular canal (operating around a lateral axis inthe sagittal plane). As stated in the foregoing, the activity of thesemi-circular canals cannot be monitored directly. Instead, thevestibulo-ocular reflex is used for detecting vestibular activity duringexamination using the eye movement detector 6. If, for instance, thehead of the person being examined moves from left to right in thetransversal plane, the person's eyes will move in the opposite directionfrom right to left thanks to the vestibulo-ocular reflex. The eyemovement detector 6 records this behaviour and interprets it as ahorizontal movement vector {right arrow over (E)}_(h). If the person'shead instead is moved up and down in the sagittal plane, the person'seyes will move down and up, respectively. The eye movement detector 6records and interprets this behaviour as a vertical movement vectorFinally, if the person's head is tilted and rotated in the coronalplane, the person's eyes will rotate in the opposite direction. The eyemovement detector 6 records these eye movements and interprets thebehaviour as a rotational movement vector {right arrow over (E)}_(r).The way that the movement vectors {right arrow over (E)}_(h), {rightarrow over (E)}_(v) and {right arrow over (E)}_(r) are derived from theeye movement detector 6 is beyond the scope of this application.

The vectors {right arrow over (E)}_(h), {right arrow over (E)}_(v) and{right arrow over (E)}_(r) are also used as inputs for the calculationmodule 8 for the purpose of deriving a set of vectors indicating thepresence of a vestibular stimulus to a particular semi-circular canal.This set of vectors may be derived in the following manner:

The vectors are normalized;

${\frac{{\overset{\rightarrow}{E}}_{h}}{{\overset{\rightarrow}{E}}_{h}} = {\hat{E}}_{h}},{\frac{{\overset{\rightarrow}{E}}_{v}}{{\overset{\rightarrow}{E}}_{v}} = {\hat{E}}_{v}},{and}$$\frac{{\overset{\rightarrow}{E}}_{r}}{{\overset{\rightarrow}{E}}_{r}} = {{\hat{E}}_{r}.}$

For the left eye, a stimulus vector L is derived:

L_(lateral) = k₁Ê_(h), L_(anterior) = k₂Ê_(v) and${L_{posterior} = {k_{3}{\hat{E}}_{r}}},{\overset{\rightarrow}{L} = \begin{bmatrix}L_{lateral} \\L_{anterior} \\L_{posterior}\end{bmatrix}},$

where k₁, k₂ and k₃ are constants.

Similarly, for the right eye, a stimulus vector {right arrow over (R)}is derived:

R_(lateral) = k₁Ê_(h), R_(anterior) = k₂Ê_(v) and${R_{posterior} = {k_{3}{\hat{E}}_{r}}},{\overset{\rightarrow}{R} = {\begin{bmatrix}R_{lateral} \\R_{anterior} \\R_{posterior}\end{bmatrix}.}}$

The constants k₁, k₂ and k₃ are chosen in such a way that the individualvalues of L_(lateral), L_(anterior), L_(posterior), R_(lateral),R_(anterior) and R_(posterior) may take on the value of 0 or 1,respectively. The vectors {right arrow over (M)}, {right arrow over (L)}and {right arrow over (R)} are used by the calculation module 8 asinputs for the graphic processor 10.

During use, the graphic processor 10 takes the three-dimensionalrepresentation of a human head provided by the dedicated memory 9 andgenerates a two-dimensional representation of it by applying the vectorM to the three-dimensional representation, generating a two-dimensionalprojection angle for the representation. Next, the graphic processor 10takes the stimulus vectors {right arrow over (L)} and {right arrow over(R)}, respectively, and uses them to determine the color of theindividual semi-circular canals of the set of semi-circular canals 22Land 22R of the projection of the human head shown in the main window 20of FIG. 2. When there is no significant activity in the semi-circularcanals of the person being examined, as derived from the vectors {rightarrow over (E)}_(h), {right arrow over (E)}_(v) and {right arrow over(E)}_(r) provided by the eye movement detector 6, the semi-circularcanals are depicted in a neutral color. Upon detection of vestibularactivity in one or more of the semi-circular canals of the person beingexamined, in the manner described above, the graphic processor 10changes the color of the semi-circular canals where activity is detectedinto a color deviating from the neutral color used to illustrate novestibular activity, as illustrated by the semi-circular canals 23 and24 in FIG. 2. In this way, the head orientation and the vestibularactivity may be monitored simultaneously on the display 3 of the system1 during examination of a person wearing the rotation sensor 4 and theeye movement detector 6.

In order to provide a more secure and precise indication of the person'shead during the performance of e.g. a Dix-Hallpike maneuver, additionalindicators are provided in the main window 20 of the display 3 in theform of the horizontal reference indicator 25, the vertical referenceindicator 26 and the orientation indicator 27. The orientation indicator27 is a two-dimensional projection of a three-dimensional point P ontoan imaginary plane F in front of the two-dimensional representation of ahuman head 21. The plane F is perpendicular to the vector {right arrowover (M)}_(cal). The point P is defined as the point where the vector{right arrow over (M)}_(x,y,z) intersects with the imaginary plane F.This may be expressed as:

F=t{right arrow over (M)}_(x,y,z)=P, where tε

.

In other words, the orientation indicator 27 follows the direction ofthe head of the person being examined closely whenever the head isturned about one of its three axes. During setup of a Dix-Hallpikemaneuver, the horizontal reference indicator 25 and the verticalreference indicator 26 are projected onto the plane F in such a way thatthe orientation indicator 27 coincides with the vertical referenceindicator 26 during a first correct movement of the Dix-Hallpikemaneuver, and the orientation indicator 27 coincides with the horizontalreference indicator 25 during a second correct movement of theDix-Hallpike maneuver. The horizontal reference indicator 25 and thevertical reference indicator 26 both have an elongated shape whendisplayed in the main window 20, and this feature makes it easy for thephysician to follow with the movements of the head of the person beingexamined. By providing the system 1 with a tolerance of e.g. fivedegrees in either direction, the physician may be easily alertedwhenever a movement diverts too much from the correct movement, e.g. byhaving the orientation indicator 27 change color, texture or generalappearance in such cases, allowing the physician to perform correctionsof the movements in a secure and easy manner. The way an examination isperformed using the system 1 is described in greater detail in thefollowing.

If the Dix-Hallpike maneuver is chosen for detecting e.g. BPPV in theleft set of semi-circular canals in a person being examined, this choicemay be input to the system 1 in the test setup tab 33 in the main window20 in FIG. 2. The system 1 now shows the horizontal reference indicator25 and the vertical reference indicator 26 in the main window 20. Theperson being examined is sitting upright on an examination couch and ina first step of the Dix-Hallpike maneuver has his or her head turned 45°to the side being tested (i.e. the left side in this case). With thehead still turned in this fashion, the person is laid down on the backon the examination couch rather quickly in such a way that the head istilted further 20°-30° backwards. During this part of the Dix-Hallpikemaneuver, the physician performing the maneuver watches the main window20 on the display 3, especially keeping an eye on the orientationindicator 27. The orientation indicator 27 moves about in the mainwindow 20 when the head of the person being examined moves, and usuallyrepresents the gaze direction of the person. If the head angle differstoo much from the expected 45°, or if the movement of the person beingexamined into the lying position is too slow, the orientation indicator27 in the main window 20 changes color, e.g. to a red color, in order toguide the physician to a proper execution of the movement. During asecond step of the Dix-Hallpike maneuver, the person being examined isreturned to an upright sitting position while keeping the head turned45° to the left, the physician still keeping an eye on the orientationindicator 27 in order to provide the right velocity and angles for thesecond step of the Dix-Hallpike maneuver.

During the performance of the Dix-Hallpike maneuver, the system 1records and displays the movements and reactions of the person beingexamined. The head angle is reflected in the two-dimensionalrepresentation of a human head 21 in the main window 20 allowing thephysician to follow the head orientations in a precise manner duringexamination. The reactions of the vestibular systems of the person beingexamined are being reflected in the two-dimensional representation ofthe semi-circular canals 22L and 22R displayed along with the human headrepresentation 21, allowing the physician to monitor the vestibularreactions of the person being examined in real time during examination.The horizontal reference indicator 25 and the vertical referenceindicator 26 provides a guidance for the physician performing themovements of the Dix-Hallpike maneuver, using the positioning andcoloring of the orientation indicator 27 as an aid in the movements.

When the Dix-Hallpike maneuver has been performed, the physician maybrowse through the recorded data by selecting the “Collection” tab 35 ofthe main window 20 and perform subsequent analyses aided by the recordeddata set in order to establish accurate diagnoses, e.g. of BPPV. Themechanism of the aid provided by the system 1 is described more closelywith reference to FIGS. 3a and 3 b.

In FIG. 3a is illustrated an orientation indicator 27 right afterperformance of a first step in a Dix-Hallpike maneuver. As stated in theforegoing, the first step of a Dix-Hallpike maneuver involves turningthe head of the person being examined 45° from the origin about thevertical axis towards the suspected affected side, in this case the leftside, while keeping the head straight up. The orientation indicator 27will move about in the display 3 as the head is turned, in this case tothe left side. In FIG. 3a , the orientation indicator 27 is at the 45°mark on the horizontal axis and at 0° on the vertical axis. Also shownin FIG. 3a is a vertical box V and a horizontal box H. As indicated inFIG. 3a , these boxes represents the horizontal reference indicator 25and the vertical reference indicator 26 in FIG. 2 and illustrate thelimits within which the orientation indicator 27 is deemed to be‘correctly’ positioned horizontally and vertically. As long as thecenter of the orientation indicator 27 is within those limits, theorientation indicator 27 is assigned a pale, or neutral color by thesystem when shown in the main window 20 in FIG. 2. The rotationaltolerance limits of a first step of a Dix-Hallpike maneuver is fromabout 42° to approximately 47° from the origin in the horizontal planeand from approximately −3° to around 3° from the origin in the verticalplane. These limits are selected for illustrative purposes only and arechosen arbitrarily in the examples shown in FIGS. 3a and 3 b.

In FIG. 3b is illustrated an orientation indicator 27 right afterperformance of a first step in a Dix-Hallpike maneuver. In this case,however, the physician has not turned the head of the person beingexamined sufficiently far to the left, but only to about 41° from theorigin. The orientation indicator is still at 0° along the vertical axisin FIG. 3b . Since the orientation indicator 27 is now outside thepredetermined limits defined by the vertical box V, the feedbackcondition is now met and the orientation indicator 27 is assigned adarker, contrasting color by the system when shown in the main window 20in FIG. 2, thus providing a clear feedback signal to the physician thatthe head of the person being examined has not been turned sufficientlyfar to the left in the first step of the Dix-Hallpike maneuver. As soonas the physician turns the head of the person being examinedsufficiently further to the right to have the orientation indicator 27fall within the limits of the vertical box V, the feedback conditionceases to be met and the orientation indicator 27 will therefore changeback to a neutral color in the main window 20 again. If the turn of thehead is overshot, for instance by turning the head of the person beingexamined further than approximately 47°, the feedback condition is metonce again and the orientation indicator 27 will again change to acontrasting color indicating a maneuver error by the physician.

A variety of vestibular conditions may be diagnosed or alleviated usingthe system 1. An example of a procedure which alleviates BPPV is theEpley repositioning maneuver, which works by allowing free-floatingparticles located within the affected semi-circular canal to flow backfrom the semi-circular canal to the utricle of the inner ear by thestraightforward means of gravity. The Epley maneuver involves a sequenceof manipulations with a patient similar to the Dix-Hallpike maneuver,but is a bit more involved and thus more difficult to perform correctly.Having used the system 1 and e.g. the Dix-Hallpike maneuver to determinethe extent and location of the cause of BPPV in a person, the physicianmay set up the system 1 in a similar manner in order to perform theEpley maneuver while observing the main window 20 for guidance duringthe various steps of the Epley maneuver. The physician may subsequentlyperform the Dix-Hallpike maneuver again in order to determine if, and towhat degree, the Epley maneuver have provided an improvement to thepatient.

Thanks to the elaborate guidance means provided by the main window 20 ofthe display 3 of the system 1, the physician may perform a wide range ofdifferent, vestibular examinations quickly and securely, withoutworrying if the movements performed of the person being examined ortreated are sufficiently accurate to be effective.

In a preferred embodiment, the eye movement detector 6 and the rotationsensor 4 of the system 1 are built into a pair of lightweight goggles,e.g. of the kind described in European patent application EP 14169653.4.The processing of data from the sensors of the goggles may be executedon a standard personal computer running suitable software providing thefunctionality of the computerized system 2 of the system 1. Dataacquisition, recording and storage may be provided by the standardstorage means provided by the personal computer, and means forsubsequent analysis of the data recorded during the examinations mayalso be provided by the software.

The system according to one or more embodiments described hereinprovides an improvement of diagnosis and treatment of a variety ofailments in the vestibular system of a person and is especially usefulin diagnosing and treating people suffering from BPPV.

Although particular features have been shown and described, it will beunderstood that they are not intended to limit the claimed invention,and it will be made obvious to those skilled in the art that variouschanges and modifications may be made without departing from the spiritand scope of the claimed invention. The specification and drawings are,accordingly to be regarded in an illustrative rather than restrictivesense. The claimed invention is intended to cover all alternatives,modifications and equivalents.

1. A system for detecting and recording head orientations of a person,comprising: a first sensor device capable of providing sensor dataregarding a head orientation of a person in a three-dimensional space; amedical data acquisition system configured for storing and outputtingthe sensor data from the first sensor device; and a processor configuredfor processing the sensor data from the medical data acquisition system,outputting a first signal representing the head orientation, andgenerating an image for presentation by a graphical display; wherein theimage comprises: a first reference indicator; an orientation indicator,wherein a position of the orientation indicator in the image isdetermined based on the first signal from the processor, and a feedbackindicator for providing a feedback when a first condition is met.
 2. Thesystem according to claim 1, wherein the first condition is met when thehead orientation represented by the first signal deviates more than apredetermined amount from a desired orientation according to amaneuvering scheme.
 3. The system according to claim 2, wherein themaneuvering scheme comprises a Dix-Hallpike maneuver, an Epley maneuver,or a Semant maneuver.
 4. The system according to claim 2, wherein themaneuvering scheme is pre-determined prior to detecting vestibularactivity in the person.
 5. The system according to claim 1, wherein thefirst condition is that the position of the orientation indicator in theimage deviates more than a predetermined amount from a desired positionwith relation to the first reference indicator according to amaneuvering scheme.
 6. The system according to claim 1, wherein thefeedback indicator comprises a change in a color, a shape, or a size ofthe orientation indicator.
 7. The system according to claim 1, furthercomprising a memory configured for storing a three-dimensional model ofa human head.
 8. The system according to claim 7, wherein the feedbackindicator comprises a change in a color, a shape, or a size of (1) atwo-dimensional projection of the three-dimensional model of the humanhead, (2) the first reference indicator or (3) a second referenceindicator.
 9. The system according to claim 7, wherein thethree-dimensional model of the human head comprises a firstthree-dimensional model of a left set of semi-circular canals and asecond three-dimensional model of a right set of semi-circular canals.10. The system according to claim 7, wherein the image generated by theprocessor comprises a two-dimensional projection of thethree-dimensional model of the human head, wherein a viewing angle ofthe two-dimensional projection is determined based on the first signalrepresenting the head orientation.
 11. The system according to claim 1,wherein the image generated by the processor comprises a secondreference indicator.
 12. The system according to claim 11, wherein thefirst reference indicator is configured for providing a first feedbackregarding a first rotation about a first local axis, and the secondreference indicator is configured for providing a second feedbackregarding a second rotation about a second local axis perpendicular tothe first local axis.
 13. The system according to claim 1, furthercomprising a second sensor device capable of providing an additionalsensor data regarding an eye movement of the person.
 14. The systemaccording to claim 13, further comprising a memory configured forstoring a three-dimensional model of a human head; wherein thethree-dimensional model of the human head comprises a firstthree-dimensional model of a left set of semi-circular canals, and asecond three-dimensional model of a right set of semi-circular canals;and wherein the processor is configured to (1) provide a two-dimensionalprojection of the first three-dimensional model, the secondthree-dimensional mode, or both, and (2) to change a color of at least apart of the two-dimensional projection in response to a derivedvestibular activity.
 15. The system according to claim 1, furthercomprising the graphical display.
 16. The system according to claim 13,wherein the processor is configured for deriving vestibular activityfrom the additional sensor data regarding the eye movement provided bythe second sensor device.
 17. The system according to claim 13, whereinthe processor is configured to generate feedback signal based on thesensor data from the first sensor device, and the additional sensor datafrom the second sensor device.